1. Field of the Invention
The present invention relates to a process for determining the presence or absence of a possibility that a vehicle is overturned laterally or sideways, based on a rolling angle and a rolling angular speed of the vehicle.
2. Description of the Related Art
On a two-dimensional map made using a rolling angle and a rolling angular speed of a vehicle used as parameters, a lateral overturning region is established in an area where the rolling angle and the rolling angular speed are larger (i.e., an area farther from an origin), and a lateral non-overturning region is established in an area where the rolling angle and the rolling angular speed are smaller (i.e., an area including the origin). A process for determining the possibility of the lateral overturning of a vehicle is known from Japanese Patent Application Laid-open No. 7-164985. According to the known process, when a hysteresis line made by plotting actual rolling angles and actual rolling angular speeds on the map has entered into the lateral overturning region from the lateral non-overturning region, it is determined that there is a possibility that the vehicle is overturned laterally or sideways, and an active roll bar is raised.
When a vehicle is rolled largely leftwards to reach a fully bumping rolling angle, for example, because a steering wheel has suddenly been operated leftwards in a course of a driving operation such as a double-lane changing operation, a suspension spring for a left wheel may be contracted to a limit, and a suspension spring for a right wheel may be expanded to a limit. When the left and right suspension springs are contracted and expanded to the limits in the above manner, a buffering effect for a rolling moment provided by the resilience of the suspension springs is lost. For this reason, there is a possibility that the leftward rolling angular speed is increased sharply, and as a result, the vehicle laterally overturns. Such lateral overturning due to a rolling resonance phenomenon occurs suddenly. Therefore, in the determination using a lateral overturning region and a lateral non-overturning region established on a usual two-dimensional map, there is a possibility that a delay is produced and thus, an occupant restraint device such as an air curtain cannot be operated with a proper timing.
When a tire has collided against a curb or the like in a course of side slipping of the vehicle, the rolling angular speed may be increased sharply by a rolling moment about the tire and as a result, the vehicle may be overturned laterally or sideways in a short time. In the lateral overturning of a type called xe2x80x9ctrip-overxe2x80x9d, an occupant on a seat is moved to an outer side of a vehicle body (toward a door) by inertia at a time point when the tire has collided against the curb or the like, resulting in a reduced sideslip speed. For this reason, the smooth deployment of an air curtain to be deployed along an inner surface of a door or an air bag to be deployed upon side-collision of the vehicle may be obstructed in some cases. Therefore, when the tire has collided against the curb or the like, it is necessary to early presume the occurrence of the lateral overturning of the xe2x80x9ctrip-overxe2x80x9d type to operate the occupant restraint device quickly.
The above known process suffers from a problem that as long as the hysteresis line for the rolling angle and the rolling angular speed indicating the operational state of the vehicle exists in the lateral non-overturning region on the two-dimensional map, even if intended driving causing the hysteresis line to be extremely close to the lateral overturning region is repeatedly conducted, a driver does not notice this fact and does not moderate his/her driving. In addition, when a lateral overturning accident of the vehicle has occurred, it is extremely difficult to verify later how the rolling angle and the rolling angular speed are varied, and which resulted in the lateral overturning of the vehicle.
Accordingly, it is a first object of the present invention to ensure that in the determination of the presence or absence of a possibility of lateral overturning of a vehicle based on a rolling angle and a rolling angular speed of the vehicle, the lateral overturning due to a rolling resonance phenomenon can be coped with.
It is a second object of the present invention to ensure that in the determination of the presence or absence of a possibility of lateral overturning of a vehicle based on a rolling angle and a rolling angular speed of the vehicle, the lateral overturning of the xe2x80x9ctrip-overxe2x80x9d type occurring upon collision of a tire against a curb or the like can be detected earlier.
It is a third object of the present invention to ensure that in the determination of the presence or absence of a possibility of lateral overturning of a vehicle based on a rolling angle and a rolling angular speed of the vehicle, the hysteresis line for the rolling angle and the rolling angular speed can be confirmed later.
To achieve the above first object, according to a first aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the step of establishing a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, so that when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold value line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, and wherein when the rolling angular speed is increased after the rolling angle has reached a fully-bumping rolling angle while the rolling angular speed was decreased, the threshold value line is moved toward the origin.
With the above feature, when the rolling angular speed is increased after the rolling angle has reached the fully-bumping rolling angle while the rolling angular speed of the vehicle was decreased, it is determined that the vehicle is in a state in which the lateral overturning due to a rolling resonance phenomenon is liable to occur, whereby the threshold value line is moved toward the origin. Therefore, it is possible to ensure that the hysteresis line for the rolling angle and the rolling angular speed easily traverses the threshold value line from the lateral non-overturning region to the lateral overturning region, whereby the determination of the presence of the lateral overturning can be conducted earlier.
To achieve the above second object, according to a second aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the step of establishing a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, so that when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold value line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, and wherein the threshold value line is moved in accordance with a differentiation value of the rolling angular speed with regard to the rolling angle.
With the above feature, when the vehicle side-slips, causing a tire to collide against a curb or the like on a road, thus suddenly reaching the condition of lateral overturning, a feature of the differentiation value of the rolling angular speed with regard to the rolling angle being increased appears on the two-dimensional map made using the rolling angle and the rolling angular speed as the parameters. With this point in view, it is possible to properly conduct the determination that there is a possibility of a lateral overturning of a xe2x80x9ctrip-overxe2x80x9d type by moving the threshold value line in accordance with the differentiation value.
To achieve the second object, according to a third aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the step of establishing a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, so that when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold value line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, and wherein the threshold value line is moved in accordance with a time-differentiation value of the rolling angular speed.
With the above feature, when the vehicle side-slips, causing a tire to collide against a curb or the like on a road, thus suddenly reaching the condition of lateral overturning, a feature of the differentiation value of the rolling angular speed with regard to the rolling angle being increased appears on the two-dimensional map made using the rolling angle and the rolling angular speed as the parameters. With this point in view, it is possible to properly conduct the determination that there is a possibility of a lateral overturning of a xe2x80x9ctrip-overxe2x80x9d type by moving the threshold value line in accordance with the differentiation value.
To achieve the third object, according to a fourth aspect and feature of the present invention, there is provided a process for determining the lateral overturning of a vehicle, comprising the step of establishing a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle as parameters, so that when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold value line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, wherein a data-storing region adjacent the threshold value line is established in the lateral non-overturning region, and when the hysteresis line has entered into the data-storing region, this hysteresis line is stored.
With the above feature, when the hysteresis line for the rolling angle and the rolling angular speed of the vehicle has entered into the data-storing region established adjacent the side of the threshold value line nearer to the origin, such hysteresis line, or the portion thereof in the data-storing region, is stored. Therefore, the stored hysteresis line can be read later to confirm whether the driver""s driving operation is/was proper. In addition, even when the vehicle has been overturned laterally, the hysteresis line within the data-storing region is stored and hence, it is possible to easily verify later how the vehicle reached the condition of lateral overturning.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.